1. Field of the Invention
This invention relates to a catalyst suitable for use in a fluid catalytic process and a method of using the catalyst on hydrocarbons containing one or more soluble metal poisons (vanadium, nickel or iron) to convert the hydrocarbons to lower boiling fractions. The catalyst contains one or more particulate, discrete, substantially water-insoluble strontium compounds (in addition to a conventional zeolite and catalyst matrix) which react with and trap the metal poison to preserve the structure of the zeolite and, in addition, lower the coke and hydrogen production.
2. Discussion of Related Art
One major operation in the modern refinery is the process of catalytic cracking. In this process, some of the heavier oils (often called "gas oils") produced upon fractionation of whole crude oil are decomposed or "cracked" using fluidized zeolite-containing catalysts. This process was developed during World War II to provide high octane gasoline for use in turbocharged fighter aircraft.
As the supply of light, sweet crude oils has dwindled during past years, catalytic cracking has become increasingly important in maintaining a supply of hydrocarbons suitable for use in various fuels such as gasoline. A problem that has occurred because of the increasing use of heavier, more sour crudes is that the heavier crudes contain substantially more organic metal compounds, such as vanadium and nickel porphyrins. These metals cause many undesirable reactions in heavy oil cracking catalysts in that the metals, specifically nickel and vanadium, are quite harmful to the fluidized cracking catalysts used. These metals, present in the high-boiling fractions, deposit on cracking catalyst and accumulate with time. They act as poisons and have the resulting effect of increasing undesirable hydrogen and coke yields and as well as decreasing the selectivity of the catalyst in making liquid products. Recently, vanadium has been found not only to increase hydrogen and coke yields but also to attack the zeolite itself, the high activity component of a catalytic cracking catalyst. See, Ritter et al, "A Look at New FCC Catalysts for Resid", Oil and Gas J., July 6, 1981, pg. 103. The mode of vanadium attack is not understood; however, available data indicate that vanadium can migrate through the catalyst particle and accumulate in areas of high zeolite concentration.
All zeolites appear to be susceptible to vanadium attack although the level of susceptibility appears to vary with the type of zeolite and its extent and type of cation exchange.
The past practice had been either to avoid charging feedstocks boiling above about 1050.degree. F. and/or limiting total metal concentrations in the feedstocks to below about 1 ppm. As noted above, these practices are no longer viable and charging heavier feedstocks containing metals is becoming increasingly necessary.
To counteract the effect of these metals, various workers have included additives such as antimony, tin, barium, calcium, manganese and bismuth into cracking catalysts to provide some measure of protection against deactivation. These so-called passivation procedures may be seen in, e.g., U.S. Pat. Nos. 3,711,422 (antimony); 3,977,963 (bismuth or manganese); 4,101,417 (tin); 4,238,362 (antimony); 4,279,735 (antimony); 4,377,494 (barium); 4,451,355 (calcium) and 4,473,463 (barium).
Other strontium compounds have been included in cracking catalysts. For instance, strontium has been ion exchanged into the zeolite, e.g., U.S. Pat. No. 3,835,030. Soluble strontium compounds, especially SrO, have been included in fluid cracking catalysts for a variety of reasons, e.g., U.S. Pat. Nos. 4,415,480; 4,382,878; 4,093,536; Ger. Offen. DE No. 2,431,983. Strontium silicate has been added as a catalyst activator. Zul'fugarov et al, "Catalyst for cracking petroleum fractions", Inst. Inorg. and Phys. Chem., Acad. of Sci., Azerbaidzhan S.S.R., (1980).
Catalytic cracking catalysts have been treated with water-soluble, non-particulate compounds to alleviate problems associated with vanadium containing feedstocks. See, WP No. 8203225 or U.S. Pat. No. 4,432,890.
None of the cited prior art references suggests a catalyst containing particulate, substantially water-insoluble strontium materials as an effective method for mitigating the deleterious effects of nickel and vanadium contained in catalytic cracking feedstocks.